1. Field of the Invention
The present invention relates to a control method of an electric rotating machine for vehicle installed in an internal combustion engine for vehicle and used as a generator and a motor.
2. Description of the Related Art
Hitherto, it has been proposed that a three-phase synchronous rotating machine is mounted on a vehicle and used as a charging generator in driving the vehicle as well as a starting motor in starting the internal combustion engine. Vehicles adopting idle stop, i.e., a function of stopping the internal combustion engine during stopping the vehicle in order to reduce exhaust gas, have been available recent years. In these vehicles, especially when the vehicle is stopping on the red light, it is necessary to complete restart of the internal combustion engine so that the vehicle is ready to start immediately upon receipt of a command to restart the internal combustion engine on the green light.
However, in a case where the electric rotating machine is used both as a charging generator and as a starter motor, a field winding of an electric rotating machine requires a large time constant as described later in order to satisfy the function as the charging generator. As a result, when such an electric rotating machine is used to perform a function as a motor, rise time of the field current is used to be long and it takes a long time to restart the internal combustion engine, and the vehicle cannot start smoothly. Means for solving such a problem is disclosed in such literatures as Patent Document 1 (the Japanese Patent Publication (unexamined) No. 2002-19158, page 4, FIG. 4) and Patent Document 2 (the Japanese Patent Publication (unexamined) No. 313498/1999 pages 3 to 7, FIGS. 7 and 8).
Patent Document 1 discloses an art in which when an internal combustion engine is started by a synchronous generator motor having a field winding and an armature winding, a power converter supplies the armature winding with an armature current having a current component that forms magnetic flux in the same direction as field flux generated by the field winding. Patent Document 2 discloses an art related to a synchronous motor for a hybrid car, in which delay in rising torque due to delay in rising field current is compensated by the steps of: detecting that the synchronous motor is in a transient state, i.e., the synchronous motor is not rotating at a constant speed during driving the synchronous motor; obtaining a current component for getting a magnetic flux whose component is coaxial with field flux on the basis of an output demand value; and controlling the armature current based on the obtained current component.
In the foregoing conventional arts, particularly in Patent Document 1, an electric current is applied to the armature (a stator) so as to generate magnetic flux in the same direction as the field flux (rotator flux). As a result, the iron core forming a magnetic circuit of a magnetic field is saturated, and self-inductance of the field winding is reduced. The time constant is decreased and the rise time of the field current is shortened, and responsiveness of the synchronous motor is improved. However, the synchronous machine controlled as described above still has problems as described below.
When electric supply is abruptly started so that magnetic flux is generated in the same direction as the field flux in the armature, an induced electromotive force is generated in the field winding in the direction to cancel the magnetic flux. Generally a control circuit for controlling the field current is provided with a semiconductor control device (numeral 301) as shown in FIG. 3 of Patent Document 1. The mentioned induced electromotive force is an electromotive force in a direction opposite to the current that is originally applied to the field winding. As the electromotive force reaches a relatively high voltage, it is necessary to increase withstand voltage of the semiconductor control element more than required. Moreover, in a case where a two-way device capable of applying a current bidirectionally is used as the semiconductor control element in order to control the counter electromotive force, a current flows in a direction opposite to the original field current. This brings about a bias resulting in delay of the rise time of the field flux.
To meet these problems, it may be an idea to start up the field current after the current applied to the armature has reached a predetermined value. In this case, however, the time for applying a power to the armature becomes longer. Hence a problem exists in that temperature rise occurs in the control circuit that controls the armature winding and application of current to the armature winding. Moreover, a synchronous machine for starting the internal combustion engine has been used. In this synchronous machine, field winding and permanent magnet are used together and a part of the magnetic flux of the permanent magnet is generated in a direction opposite to the main magnetic flux generated by the field winding in order to restrain magnetic saturation and leakage flux of the field winding. In the case of applying the mentioned conventional art to such a synchronous machine, it is essential to increase the current applied to the armature in order to saturate the magnetic circuit of the magnetic field. Since total sum of the field magnetomotive force is large particularly in the Randell-type multi-polar synchronous rotating machine, the temperature rise in the armature winding and the current control circuit is increased all the more.